B122 - Panel Dimming Switch Pot Circuit

Code B122 - Panel Dimming Switch:

Wiring Diagram for Codes B119, B120, B121, B122 & B123:

CODE B122 - PANEL DIMMING SWITCH POT CIRCUIT

Circuit Desctiption:

The panel dimmer uses a potentiometer to control the signal voltage to the BCM. The BCM supplies voltage on circuit 705 to the resistor in the left switch assembly and returns as a grounds to the BCM on circuit 736. The wiper provides the voltage signal to the BCM on circuit 686 indicating position of the slider and dim level. When the slider is moved toward the max. (bright) position, resistance is high, therefore the BCM will see a low signal voltage. As the slider is moved toward the min. (dim) position the resistance becomes less and the signal voltage increases. This signal voltage will vary between OV (open or grounded CKT.) and 5V (shorted to voltage).

Code B122 will set if the ignition is on and the signal voltage indicates less than 6% (open or grounded CKT) or over 94% (shorted to voltage). During the time the failure is present a substitute dimming value will be implemented to allow continued operation of interior lighting. The reading from the potentiometer BD42 however, will display the actual reading.


Test Description:

1. BCM data value BD42 displays the panel dimming levels. The normal range is from 6 to 94%.

2. Checks to see if the open or grounded circuit reading is due to the circuit or switch assembly. If the open or grounded circuit reading changes to a short to voltage reading after jumpering the switch assembly terminals, the BCM and wiring are OK.

3. Measuring (5 volts) voltage between CKT 705 and 686 will determine if CKT 686 is open or shorted to ground.

4. Checks to see if the short to voltage circuit reading is due to the circuit or switch assembly. If a short to voltage reading changes to an open circuit reading after disconnecting the switch assembly, the BCM and wiring are OK.


Note on Intermittents:

If an intermittent Code B122 is being set, manipulate the related wiring while observing BCM data value BD42. If the failure is induced, the reading will jump from its normal value to a reading outside the range of 6 to 94%.